Radio-controlled timepieces provided with a radio function such as a personal-computer communication function, a cellular phone function, anon-contact IC-card function or the like have been known. As such wireless function watches, radio controlled watches which receive a standard long wave (carrier wave) containing time information and modify the time based on the time information are also widely known.
These wireless function watches are required to be provided with an antenna for receiving a predetermined radio wave, similarly to other communication equipment.
From the viewpoint of the receiving sensitivity that is a function of receiving a radio wave, a housing that accommodates an antenna for receiving a radio wave may be constituted of a non-conductive material such as a synthetic resin.
However, since these wireless function watches are watches, esthetic or high-class appearance as ornaments or accessories is required unlike other communication equipment.
Thus, a housing that accommodates an antenna for receiving a radio wave should be made of a conductive material, that is, a metal material, not a non-conductive material such as a synthetic resin. This is because a housing made of a synthetic resin gives a cheap appearance and a cheap feeling of wearing to a wearer due to its texture, tone or lightness. The demand for metal housings is particularly remarkable in watches as accessories worn by users.
However, in the case where an outer case and a caseback of such a wireless function watch are formed of metal and a dial plate is also formed of metal, the antenna is accommodated in a closed space completely shielded by the metal members, and a radio wave reaching the antenna is attenuated by the metal members. As a result, there is a problem that a required and sufficient receiving sensitivity as a wireless function watch cannot be obtained.
That is, as shown in FIG. 49, when a radio wave 104 is incident on an antenna 102 in a wireless function watch 100, an antenna core portion 106 transmits the wave 104, then a magnetic field is generated around the antenna 102, and an electric current is generated in an antenna coil 108. But if a large metal member which easily transmits magnetism is disposed in the vicinity of the antenna 102, part of the magnetic field generated around the antenna 102 is absorbed by the metal member nearby. As a result, the resonance of the antenna 102 is prevented, and a required and sufficient receiving sensitivity cannot be obtained.
Therefore, Patent Document 1 discloses a wireless function watch 100 in which a dial plate 112 that forms one of the faces of a closed space 110 accommodating an antenna 102, and a solar cell 116 held between the dial plate 112 and a watch movement 114 are formed of a non-metal material which easily transmits a radio wave. In FIG. 49, reference numeral 118 denotes an attenuated wave, reference numeral 120 denotes glass, reference numeral 122 denotes a bezel, reference numeral 124 is an outer case, and reference numeral 126 is a caseback.
According to the wireless function watch 100, a required and sufficient receiving sensitivity can be ensured even if a metal exterior is used.
Patent Document 2 discloses a radio-controlled wrist watch 200 as shown in FIG. 50, having a loop antenna 202 for receiving a radio wave, a first watch case 206 having a side face and made of a non-conductive material wherein the case accommodates the loop antenna 202 so that loop open faces 204, 204 of the loop antenna 202 are opposed to the side face, and a second watch case 210 attached so as to cover the outer side of the first watch case 206 and made of a metal material in which an opening 208 is formed in at least one of the locations opposed to the loop open faces 204, 204 of the loop antenna 202. In FIG. 50, reference numeral 212 denotes a dial plate and reference numeral 214 denotes a caseback.
The radio-controlled wrist watch 200 is configured such that in the second watch case 210 the openings 208, 208 are formed at locations opposed to the loop open faces 204, 204 of the loop antenna 202 so that a standard long wave can reach the loop open faces 204, 204 of the loop antenna 202 through the openings 208, 208.
By using the second watch case 210 in which the openings 208, 208 are formed at locations opposed to the loop open faces 204, 204 of the loop antenna 202, a standard long wave can be received by the loop antenna 202 even if the second watch case 210 made of a metal material, which is a conductive material, covers the first watch case 206 except the locations opposed to the loop open faces 204, 204.
The loop antenna 202 has the same shape as a bar-shaped bar antenna used as one of embodiments of the invention.
If a watch case and a caseback are formed of metal, a radio wave from outside is incident on the antenna mainly through a glass glass and a non-conductive dial plate.
However, a metal dial plate is often used in order to improve esthetic and high-class appearance as a watch. In this case, since the dial plate is made of metal, a good-appearance dial plate can be easily realized at low cost, but a radio wave incident from outside is shielded and attenuated by the metal dial plate.
In relation to this problem, Patent Document 3 discloses an radio controlled watch 300 as shown in FIGS. 51 and 52 wherein a receiving antenna 326 is located at a position opposed to an opening 333 provided in a metal dial plate 324 so that a radio wave entering a case 314 through the opening 333 is reliably received by the receiving antenna 326. Even though the dial plate 324 is made of metal, the decrease of a receiving sensitivity for the standard wave can be minimized.
In the wireless function watches as described above, if the watch case 124 or 210 is made of a conductive material, incident of a radio wave on the wireless function watch causes the generation of an eddy current as an induction current along a circumferential direction of an annular wall of the conductive watch case 124 or 210.
If the eddy current is generated as above, the eddy current offsets the wave from outside and the receiving sensitivity of the antenna 106 or 202 is decreased.
In order to avoid such a phenomenon, Patent Document 4 discloses a wireless function watch 400 wherein a slit 432 dividing a watch case 414 in the circumferential direction is provided in an annular wall of the watch case 414. That is, as shown in FIG. 53, the watch case 414 is completely divided in the vertical direction by the slit 432 so as to form a substantially C-shaped frame as a result.
In FIG. 53, though not shown, an insulating member made of a synthetic resin is incorporated in the slit 432, and water-proof properties and strength are ensured by the insulating member.
According to the wireless function watch 400 in which the slit 432 is formed in the axial direction of the watch case 414, an eddy current does not flow along the circumferential direction of the annular wall of the watch case 414 when the antenna 426 receives a radio wave from outside. Therefore, even with the housing 412 provided with the metal watch case 414, the antenna 426 inside can receive the radio wave.    Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2004-340700    Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2003-161788    Patent Document 3: Japanese Patent Application Laid-Open Publication No. 2006-189379    Patent Document 4: Japanese Patent Application Laid-Open Publication No. 2002-341057
Although the wireless function watch described in Patent Document 1 has improved receiving sensitivity by forming the dial plate and the solar cell from a non-metal material, the antenna cannot often receive a radio wave depending on a location where the wireless function watch is placed or depending on the surrounding environment or the posture of the watch.
Therefore, even with the wireless function watch in which the dial plate and the solar cell are formed of a non-metal material as in Patent Document 1, the receiving sensitivity of the antenna can hardly obtain sufficient receiving sensitivity yet. Thus, wireless function watches with improved receiving sensitivity are demanded.
In the radio-controlled wrist watch described in Patent Document 2, since an opening is provided in the first watch case on the outermost side, the inner second watch case made of a non-conductive material is seen through the opening, which damages appearance and high-class appearance. Moreover, since the inner second watch case is made of a non-conductive material, the watch is not a so-called full-metal radio-controlled wrist watch in which all the exterior parts are made of metal.
Further, since the watch cases form a double structure, the thickness in the radial direction is large and the size of the watch is excessively large.
Moreover, when the radio-controlled wrist watch is worn, the opening is brought into contact with skin, which causes bad wearing feeling and discomfort.
In the radio-controlled watch described in Patent Document 3, since the antenna is usually located adjacent to an outer circumferential portion of the movement, a projection portion or a dial ring that is not shown is present above the antenna as shown in FIG. 52. Thus, it is difficult to provide an opening in the dial plate at a position opposed to the antenna. If the opening is provided in the dial plate off the position opposed to the antenna, sufficient receiving sensitivity of the antenna cannot be obtained.
In the wireless function watch described in Patent Document 4, since the insulating member made of a synthetic resin is incorporated in the slit 432 of the watch case 414, appearance is not favorable and high-class appearance is insufficient. When compared with a watch case entirely formed of metal, it is unavoidable that strength is weaker at a portion where the insulating member is incorporated, and water-proof properties, impact resistance and chemical resistance are deteriorated.
Further, depending on a location where the wireless function watch 400 is placed or depending on the posture of the wireless function watch 400, the antenna 426 cannot often receive a radio wave sufficiently.
As mentioned above, even with the wireless function watch 400 in which the slit 432 in the height direction is formed in the annular wall of the watch case 414, the antenna 426 can hardly obtain sufficient receiving sensitivity yet.
Moreover, some wireless function watches are provided with a dial ring 536 in a watch case 514, as a wireless function watch 500 shown in FIG. 54.
The dial ring 536 is arranged between a glass 518 made of glass and a dial plate 524 in the watch case 514, and is a ring-shaped member provided with a stadium-shaped face inclined inward in the radial direction. An upper face of the dial ring 536 is a mounting face for the glass 518, and the inclined face extending downward from the upper face toward the dial plate 524 functions as an index face on which indexes indicating function display of the watch are arranged.
The dial ring 536 is made of metal or is composed of a synthetic resin member coated with a metal film, in order to achieve esthetic appearance or high-class appearance as an accessory similar to the watch case 514.
Specifically, the wireless function watch 500 shown in FIG. 54 is provided with a substantially cylindrical watch case 514 made of metal and having open ends in the vertical direction, a caseback 516 made of metal and attached on the lower-face opening of the watch case 514 so as to seal the watch case through a water-proof packing 547, and a glass 518 made of glass and attached on the upper-face opening of the watch case 514 so as to seal the watch case through a water-proof packing 546. A housing 512 is thus configured. That is, in the wireless function watch 500, a cylindrical portion with a bottom of the housing 512 except the glass 518 is composed of metal.
In the housing 512 of the wireless function watch 500, a movement 520 constituting a watch driving portion, a solar cell 522, and a dial plate 524 provided with a light transmitting function are accommodated. Moreover, an antenna 526 is attached below and aside the movement 520.
In the wireless function watch 500 with such configuration, the watch case 514 and the caseback 516 are integrated by the engagement of an engaging projecting portion 550 of a core member 548 projecting inward from the caseback 516 with an engaging recess portion 552 formed on the inner circumferential side in the vicinity of the lower end of the watch case 514. At a tip end portion of the core member 548, an annular support frame 554 made of a non-conductor is arranged.
In the wireless function watch 500, the movement 520, the solar cell 522 and the dial plate 524 are positioned and fixed by a flange-shaped dial ring receiving portion 532 formed inward in the radial direction at the upper opening side of the watch case 514, and the support frame 554 arranged on the core member 548.
When the conductive dial ring 536 is arranged on the conductive watch case 514 as mentioned above, electricity is conducted through the dial ring 536 even if the slit 522 is formed. Therefore, the receiving sensitivity of the antenna 526 cannot be improved.
The present invention was made in view of the current circumstances. It is therefore an object of the invention to provide a wireless function watch which has a favorable receiving sensitivity even with a full-metal structure and can reliably receive a predetermined radio wave with the antenna.
The present invention has another object to provide a wireless function watch which has an appearance similar to a (usual) watch not having an antenna and has esthetic appearance, high-class appearance and excellent strength.
The present invention has another object to provide a wireless function watch with favorable wearing feeling.
The present invention has another object to provide a wireless function watch without a need to excessively increase a thickness in the radial direction.